Constant voltage float charge rectifier and battery surveillance circuits, including two-level constant voltage float charge rectifier and battery surveillance apparatus, are well known in the industry. The present inventor has provided several circuits and apparatus for battery charging in the past, including a circuit having an initial constant, high current output, which then transfers to a taper (constant voltage) output, and finally to a trickle (constant current) charge. That circuit is described in detail in HASE, U.S. Pat. No. 3,848,173, issued Nov. 12, 1974.
A further battery charger circuit, having full-time surveillance, is described in detail in HASE, U.S. Pat. No. 4,320,333, issued Mar. 16, 1982.
Yet a further, improved two-level battery charging circuit is described in detail in HASE, U.S. Pat. No. 4,399,396, issued Aug. 16, 1983.
It is well recognized that it may be desirable for there to be such surveillance of a battery charging sequence by battery charging circuits so as to provide an immediate indication that the charging sequence is in operation or that it has reached the trickle charge condition whereby the battery is substantially fully charged. Moreover, it may be desirable to provide an indication as to when the gassing point of the battery is reached, nominally and substantially at the point when the battery has received 80% of its charge--a condition at which the battery may be disconnected and put back into service, although such action is not recommended. It is also desirable for there to be an annunciation when there may be a battery problem, for example a shorted battery cell which absorbs higher rates of energy input beyond a time when a normal battery would have been charged so that the taper charging or trickle charging portions of a battery charging sequence should have been initiated.
The present circuits, to a greater or lesser extent in common with previous circuits as described in some other U.S. patents issued to the inventor, as noted above, give the required and desirable circuit operating annunciations.
Moreover, especially when batteries are charged between working shifts--for example, overnight--in many circumstances such as warehouses, industrial plants, mines and the like, it is desirable to have the battery charging sequence initiated automatically at the time that the battery is connected to the battery charging circuit; and it is also desirable to preclude arcing at the connection terminals when the battery is disconnected. Very often, such batteries are used to power fork lift trucks, industrial apparatus, or the like, and they work in a very rugged environment and sometimes in circumstances where they are not gently handled. Not only are the ususal precautions of providing polarized connectors so that a battery may not be connected backwards to a battery charging circuit necessary, it has been found desirable to provide charging circuits that initiate the charging sequence merely by the act of connecting the battery to the charging circuit. It has also been found desirable to provide an annunciation by way of an illuminated lamp or other means to indicate that a battery should not be disconnected until it is at least 80% charged; and still further, to provide a means whereby the battery may be disconnected without drawing any substantial arc at the connecting terminals. The present invention provides such an arrangement by presenting a push button switch which, when momentarily depressed, causes the output voltage from the charging circuit to reduce and thereby reduces any output current to a leakage current at best. Of course, it is recognized that the power diodes in a charging circuit then act to block the circuit from becoming a load on the battery, and thereby to preclude discharge from the battery.
At the same time, provision of magnetic shut down--by which the operation of the synchronous switch means which controls the rate of electrical energy input to the storage battery, is substantially arrested, to make the circuit operation more reliable and so that there is substantially no energy transfer across the input transformer to the battery charger--precludes the necessity for providing electro-mechanical circuit interruptors, contactors or other mechanical and high current circuit interrupting means so as to preclude arcing damage either to the battery or the output terminals when the battery is disconnected. Thus, the additional capital expense of providing electro-mechanical circuit interruptor means is precluded, as is the additional operating expense of having to maintain and replace connectors where arcing has occurred, as with other battery charging circuits.
This is not to say, however, that it may be desirable in certain circumstances, depending on the industrial environment in which a battery charging and surveillance circuit according to the present invention is being used, to provide a hold-down means by which the battery may not be disconnected until such time as the shut-down sequence has occurred by which the output voltage of the charging circuit has been reduced below that of the battery.
It is also recognized by the present invention that a battery may be charged and used under low or high temperature extremes. For example, many industrial batteries work at all times at low temperatures such as those that are found in refrigerated warehouses, to the extent that they are not removed from such low temperature ambient even when being charged. Likewise, other industrial batteries may be at all times in or near industrial ovens or otherwise exposed to high average ambient temperatures, even when being charged. Because batteries have negative temperature co-efficients as to their internal resistance, it is therefore appropriate in some circumstances to provide an inverse temperature compensation whereby the output voltage of the charging circuit may be modulated inversely to changes of temperature when the batteries are at extremes of high or low temperature ambient conditions.
It is also desirable that, when a battery charging sequence is initiated, there should be soft walk-in, whereby when any one battery or even a number of batteries are connected to battery chargers, there is no overburden on the AC system from which battery charging energy shall be drawn. This also, therefore, precludes any in-rush currents on either the AC or DC sides of the battery chargers, or their source. When a number of high capacity batteries may be used, and power utility charges are based on peak current requirements, the requirement for soft walk-in and substantially low or no in-rush currents may become important.
It is also desirable that the solid-state devices that are used should normally be rated both as to voltage and current handling requirements at any circuit point where they may be connected, so that they are not over-stressed. Indeed, it is a feature of the present invention that the control power cut-off device that may be used in series with the control coil of the synchronous switch which controls the rate of electrical energy input, may be a low current and therefore a low heat device.
In that regard, solid-state devices that may be appropriate for use will be those that, when the operation of the circuits of the present invention are explained, may be chosen by the skilled practitioner as being those which are appropriate to the current and voltage operating characteristics at the circuit point where they will be used. Thus, the solid-state devices may be transistors, HEXFET or CMOS devices, silicon controlled rectifiers (SCR's); or indeed highly reliable, low-current relays may be used.
The above are broadly stated descriptions of certain of the features and functions of the apparatus of the present invention, discussed in greater detail hereafter.
In general terms, the present invention provides a battery charging and surveillance circuit having full-time battery and circuit operation surveillance, the circuit being adapted for connection at its input to a source of alternating current electrical energy and at its output to a storage battery. At its input, the circuit has a synchronous switch means having a control coil--which may be a saturable reactor, a magnetic amplifier, equivalent SCR circuitry, or otherwise--whereby operation of the control coil controls the rate of electrical energy input to the storage battery when it is connected to the circuit. The act of connecting the storage battery to the output terminals of the charging circuit automatically initiates a battery charging sequence, as discussed in detail hereafter.
In keeping with the present invention, an auxiliary power supply circuit is found within the charging circuit across the output thereof, which auxiliary power supply circuit is subjected to a high ripple voltage when there is no battery load on the charging circuit. Within the auxiliary power supply there is a capacitor which may be charged to a predetermined bias voltage, and which is charged to that voltage when there is no battery connected to the output terminals of the charging circuit. Impedance means is provided to reduce the ripple voltage below a predermined level when a battery is connected to the output. A latch is provided, which is a solid-state device connected to the auxiliary power supply, and which has its base in series with a zener diode so that the predetermined bias voltage on the capacitor is the zener voltage of the zener diode plus the base-emitter voltage of the device. The bias voltage of the capacitor is sufficient to bias the solid-state device of the latch circuit to a closed, conductive, state.
A one-shot start-up circuit means is provided that has a second solid-state device that will be momentarily closed just below the zener voltage of the capacitor, when the capacitor voltage is collapsing. A control power cut-off solid-state device is provided in series with the control coil, the cut-off device being biassed to an open, non-conductive, condition when there is no battery load on the charging circuit; and a second latch is connected to the one-shot start-up circuit and to the cut-off device, the second latch being biassed to close the cut-off device when the one-shot start-up circuit closes to its conductive state.
The impedance means in the auxiliary power supply circuit acts to cause collapse of the capacitor voltage when a battery is connected to the output of the charging circuit.
There is also provided in the battery charging and surveillance circuit a momentary close switch which is connected in such a manner that, when it is closed, the second latch is biassed to a closed condition and the cut-off device is opened. Under those circumstances, the current in the control coil collapses, and therefore the output of the synchronous switch means reduces so as to reduce the output voltage of the charging circuit. When the switch is momentarily closed, and the output voltage of the charging circuit is reduced below the terminal voltage of the battery connected to the output terminals of the charging circuit, the battery may then be disconnected from the charging circuit without any substantial current flow at its connecting terminals, and therefore without arcing.
Other additional and/or optional features and operating sub-systems of the apparatus according to the present invention, as well as the principals of operation thereof, are set out hereafter.